Conventional wood framed buildings, such as residential dwellings, often include a wood-framed roof and an attic between such roof and ceiling joists of a ceiling of an upper floor of the building. In another example, a conventional attic may not be present and a cathedral type ceiling may be utilized where a ceiling is connected to roof rafters instead of a ceiling being aligned horizontally with an attic above such ceiling. It is desirable to minimize heat loss through the roof of such buildings through the use of insulation and other energy efficiency measures. By minimizing such heat loss the cost of heating and the carbon footprint of a building may be minimized.
In a conventional, wood-framed roof, a roof deck (e.g., plywood) may have shingles and other water resistant materials on an outer surface thereof and a bottom surface of the deck may be connected to roof rafters. In the case of a cathedral type ceiling, insulation (e.g., fiberglass insulation) and rafter bay baffles may be located in rafter bays between the rafters and connected to an underside of the roof deck to minimize heat loss through the roof deck.
In one example, a thermal resistance (R-value) of a 2×10 rafter is approximately R11 and for a 2×12, this may be R14. The thermal resistance of such a rafter is low for insulated roofs when compared to R-values of conventional fiberglass insulation, which ranges from around R30 installed in 2×10 rafter bays to R38 for 2×12 rafter bays. This difference may result in non-uniform heat transfer through the roof deck. Essentially, more heat will be transferred through the area in which the rafter comes in contact with the roof deck, than will be transferred through an equal area of contact between the insulated rafter bay and the roof deck. Such non-uniform heat transfer could result in non-uniform ice-melts and formation of potentially damaging ice dams.
Additionally, properly insulated rafter bays have an air space below the roof deck and above the insulation to allow for air ventilation flow between soffit and ridge vents. This air space does not extend to the area between the roof deck and the supporting rafters, exacerbating the non-uniformity in thermal resistance between the locations of the rafters and the insulated rafter bays. The presence of an air layer below the roof deck and above the insulation in the rafter bays may significantly reduce conductive heat transfer between the insulation material and the roof deck in the rafter bay areas, but have little or no effect on heat transfer in the area of contact between the rafter and the roof deck.
Thus, there is a need for systems and methods for use in increasing a thermal barrier of a roof system.